Method and system for providing a nonvolatile logic array

ABSTRACT

A method and system provide and program a nonvolatile logic device. The nonvolatile logic device includes input and output magnetic junctions and at least one magnetic junction between the input and output magnetic junctions. The input magnetic junction includes an input junction free layer having an input junction easy axis. The input magnetic junction may be switchable using a current driven through the magnetic junction. The output magnetic junction includes an output junction free layer having an output junction easy axis. Each of the magnetic junction(s) includes a free layer having an easy axis. The input magnetic junction is magnetically coupled to the output magnetic junction through the magnetic junction(s). In some aspects, the method includes switching the magnetic moment(s) of the input magnetic junction from a first state to a second state, applying and then removing magnetic field(s) along the hard axis of the at least one magnetic junction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional Patent ApplicationSer. No. 61/512,163, filed Jul. 27, 2011, assigned to the assignee ofthe present application, and incorporated herein by reference.

GOVERNMENT RIGHTS

This invention was made with U.S. Government support underGrant/Contract No. HR0011-10-C-0160 awarded by DARPA. The U.S.Government retains certain rights in this invention.

BACKGROUND

FIGS. 1A-1B depict a conventional nonvolatile logic device 10 formedusing an array of magnetic junctions 12, 14, 16, 18, 20, 22, and 24. Thejunction 12 is an input magnetic junction 12. Also shown are an outputmagnetic junction 22 and intermediate junctions 14, 16, 18, and 20. Abiasing junction 24 is also shown. However, an output electrode iscoupled with the output magnetic junction 22.

The magnetic junctions 12, 14, 16, 18, 20, and 22 are typicallytunneling magnetoresistive junctions. Thus, each junction 12, 14, 16,18, 20, and 22 typically includes a pinning layer, a pinned layer, anonmagnetic tunneling barrier layer, and a free layer. The pinned layerhas its magnetization pinned in place by the pinning layer. Themagnetizations of the free layers are shown in FIGS. 1A-1B and aretypically free to move. The junctions 12, 14, 16, 18, 20, and 22typically share a tunneling barrier layer, pinned layer, and pinninglayer. Thus, the portions of the junctions 12, 14, 16, 18, 20, and 22shown in FIGS. 1A-1B correspond to the free layer. As can be seen inFIG. 1A, the easy axis (corresponding to the shape anisotropy) for thefree layer of the input magnetic junction 12 is perpendicular to theeasy axes of the remaining magnetic junctions 14, 16, 18, 20, and 22.The remaining magnetic junctions 14, 16, 18, 20, and 22 aresubstantially identical. Thus, the magnetic junctions 14, 16, 18, 20,and 22, typically have the same shape anisotropy, magnetic moment, andother magnetic properties. The pinned layer typically has itsmagnetization oriented along the easy axis of the junctions 14, 16, 18,20, and 22. Thus, the pinned layer is oriented perpendicular to the easyaxis of the junction 12.

FIG. 1A depicts the nonvolatile logic device in a particularconfiguration. FIG. 1B depicts nonvolatile logic device 10 afterswitching to another configuration. The magnetic state of the inputdevice 12 is changed, for example by passing the current through thestructure causing spin transfer torque. An appropriate external magneticfield that saturates the magnetic junctions 14, 16, 18, 20, and 22 alongtheir hard axes is applied. The result is that the magnetic moments ofthe junctions 14, 16, 18, 20, and 22 are aligned with the saturationfield along the hard axis. As the external magnetic field is removed,the magnetic moment of the junctions 14, 16, 18, 20, and 22 cant awayfrom the hard axis. For a situation in which the external magnetic fieldis removed at an appropriate time, the moments of the junctions 14, 16,18, 20, and 22 would no longer be aligned in parallel. When the externalfield is completely removed, the state of the output junction will haveswitched because of the switch in the input junction, as is shown inFIG. 1B.

Although the conventional nonvolatile logic device 10 functions, theremay be drawbacks. If an insufficient external field is applied, then thejunctions 14. 16. 18, 20, and 22 do not saturate. The information in theinput junction 12 may then not be transferred to the output junction 22.Alternatively, if too great an external magnetic field is applied, thenthe state of the input magnetic junction 12 may be changed. In addition,the time for which the external magnetic field is applied may be desiredto be tightly controlled to ensure that switching is properly carriedout. Thus, switching of the magnetic junction 11 may be unreliableand/or subject to tight tolerances.

BRIEF SUMMARY OF THE INVENTION

A method and system provide and program a nonvolatile logic device. Thenonvolatile logic device includes an input magnetic junction, an outputmagnetic junction and at least one magnetic junction between the inputmagnetic junction and the output magnetic junction. The input magneticjunction includes an input junction free layer having an input junctioneasy axis. The input magnetic junction may be switchable using a currentdriven through the magnetic junction. The output magnetic junctionincludes an output junction free layer having an output junction easyaxis. Each of the magnetic junction(s) includes a free layer having aneasy axis. The input magnetic junction is magnetically coupled to theoutput magnetic junction through the magnetic junction(s). In someaspects, the method includes switching the magnetic moment(s) of theinput magnetic junction from a first state to a second state, thenapplying at least one magnetic field along the hard axis of the at leastone magnetic junction. The magnetic field is then removed.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1A-1B depict a conventional nonvolatile logic device.

FIGS. 2A-2F depict cross-sectional and top views of an exemplaryembodiment of a nonvolatile logic device.

FIGS. 3A-3B depict top and cross-sectional views of another exemplaryembodiment of a nonvolatile logic device.

FIG. 4 depicts a top view of another exemplary embodiment of anonvolatile logic device.

FIG. 5 depicts a top view of another exemplary embodiment of anonvolatile logic device.

FIG. 6 depicts a top view of another exemplary embodiment of anonvolatile logic device.

FIG. 7 depicts a top view of another exemplary embodiment of anonvolatile logic device.

FIG. 8 depicts a side view of another exemplary embodiment of anonvolatile logic device.

FIG. 9 depicts a side view of another exemplary embodiment of anonvolatile logic device.

FIG. 10 depicts an exemplary embodiment of a method for providing anonvolatile logic device.

FIG. 11 depicts an exemplary embodiment of a method for providingproviding a nonvolatile logic device.

FIG. 12 depicts an exemplary embodiment of a method for programming anonvolatile logic device.

DETAILED DESCRIPTION OF THE INVENTION

The exemplary embodiments relate to nonvolatile devices and magneticjunctions usable in such nonvolatile devices. The following descriptionis presented to enable one of ordinary skill in the art to make and usethe invention and is provided in the context of a patent application andits requirements. Various modifications to the exemplary embodiments andthe generic principles and features described herein will be readilyapparent. The exemplary embodiments are mainly described in terms ofparticular methods and systems provided in particular implementations.However, the methods and systems will operate effectively in otherimplementations. Phrases such as “exemplary embodiment”, “oneembodiment” and “another embodiment” may refer to the same or differentembodiments as well as to multiple embodiments. The embodiments will bedescribed with respect to systems and/or devices having certaincomponents. However, the systems and/or devices may include more or lesscomponents than those shown, and variations in the arrangement and typeof the components may be made without departing from the scope of theinvention. The exemplary embodiments will also be described in thecontext of particular methods having certain steps. However, the methodand system operate effectively for other methods having different and/oradditional steps and steps in different orders that are not inconsistentwith the exemplary embodiments. Thus, the present invention is notintended to be limited to the embodiments shown, but is to be accordedthe widest scope consistent with the principles and features describedherein.

The exemplary embodiments are described in the context of particularmagnetic junctions and nonvolatile logic devices having certaincomponents. One of ordinary skill in the art will readily recognize thatthe present invention is consistent with the use of magnetic junctionsand nonvolatile logic devices having other and/or additional componentsand/or other features not inconsistent with the present invention. Themethod and system are also described in the context of currentunderstanding of the spin transfer phenomenon, of magnetic anisotropy,and other physical phenomena. Consequently, one of ordinary skill in theart will readily recognize that theoretical explanations of the behaviorof the method and system are made based upon this current understandingof spin transfer, magnetic anisotropy and other physical phenomena.However, the method and system described herein are not dependent upon aparticular physical explanation. One of ordinary skill in the art willalso readily recognize that the method and system are described in thecontext of a structure having a particular relationship to thesubstrate. However, one of ordinary skill in the art will readilyrecognize that the method and system are consistent with otherstructures. In addition, the method and system are described in thecontext of certain layers being synthetic and/or simple. However, one ofordinary skill in the art will readily recognize that the layers couldhave another structure. Furthermore, the method and system are describedin the context of magnetic junctions and/or substructures havingparticular layers. However, one of ordinary skill in the art willreadily recognize that magnetic junctions and/or substructures havingadditional and/or different layers not inconsistent with the method andsystem could also be used. Moreover, certain components are described asbeing magnetic, ferromagnetic, and ferrimagnetic. As used herein, theterm magnetic could include ferromagnetic, ferrimagnetic or likestructures. Thus, as used herein, the term “magnetic” or “ferromagnetic”includes, but is not limited to ferromagnets and ferrimagnets. Themethod and system are also described in the context of single magneticjunctions and substructures. However, one of ordinary skill in the artwill readily recognize that the method and system are consistent withthe use of magnetic memories having multiple magnetic junctions andusing multiple substructures. Further, as used herein, “in-plane” issubstantially within or parallel to the plane of one or more of thelayers of a magnetic junction. Conversely, “perpendicular” correspondsto a direction that is substantially perpendicular to one or more of thelayers of the magnetic junction.

FIGS. 2A and 2B-2F depict a side view and top views of a nonvolatilelogic device 100. The nonvolatile logic device 100 may be combined withlike devices the appropriate electrical connection to form logic gates,such as NOT, AND, NAND, OR, and/or NOR gates. Referring to FIGS. 2A-2B,the nonvolatile logic device includes a bottom electrode 102 and anoutput electrode 118. The nonvolatile logic device includes magneticjunctions 120, 122, 124, 126, 128, 130, and 132. The magnetic junction120 is an input magnetic junction. Information is input to thenonvolatile logic device 100 via the magnetic junction 120 by passingthe current through junction 120. This current exerts spin transfertorque on the input magnet and switches its magnetization to the state,which depends on the direction of the applied current. The magneticjunction 130 is an output magnetic junction. Thus, an electrode 118 isalso provided for the output magnetic junction 130. By reading theresistance of the magnetic junction 130, the state of the nonvolatilelogic device 100 may be determined. The magnetic junction 132 is abiasing junction. The magnetic junctions 122, 124, 126, and 128 residebetween the input magnetic junction 120 and the output magnetic junction130. In the embodiment shown, four magnetic junctions 122, 124, 126, and128 are shown. However, in another embodiment, another number ofmagnetic junctions may be provided between the input magnetic junction120 and the output magnetic junction 130. The input magnetic junction120 is coupled with the output magnetic junction 130 through theremaining magnetic junctions 122, 124, 126, and 128.

The magnetic junctions 120, 122, 124, 126, 128, 130, and 132 share abottom electrode, optional pinning layer 104, pinned layer 106, andspacer layer 114. The free layers of the magnetic junctions 120, 122,124, 126, 128, 130, and 132 are formed from layer 116. Thus, the toplayers of the magnetic junctions 120, 122, 124, 126, 128, 130, and 132are termed nanomagnets. In the embodiment shown, the pinned layer 106 isa synthetic antiferromagnet including a pinned layer 108, a nonmagneticspacer layer 110 and a reference layer 112 that is magnetically coupledwith the pinned layer 108. In the embodiment shown, the pinned layer 108has its magnetization fixed, or pinned, by the optional pinning layer104, which may be an antiferromagnet. In other embodiments, the pinnedlayer 106 may be a single layer, another multilayer, or other structure.In the embodiment shown, the magnetizations of the layers of themagnetic junctions 122, 124, 126, 128, 130, and 132 are in plane.However, in other embodiments, the magnetization(s) may be perpendicularto plane. The spacer layer 114 is nonmagnetic and may be a tunnelingbarrier layer such as crystalline MgO. In other embodiments, the spacerlayer 114 may be conductive, or may have another structure. The layer116 may be a single, ferromagnetic layer or may be a multilayer, forexample a granular layer including conductive channels in an insulatingmatrix.

As can be seen in FIGS. 2A and 2B, the magnetic junctions 120, 122, 124,126, 128, and 130 have vertical easy axes, along which themagnetizations lie. Thus, the magnetic junctions 120, 122, 124, 126,128, and 130 have parallel easy axes. In the embodiment shown, the easyaxes of the magnetic junctions 120, 122, 124, 126 128, and 130correspond to the shape anisotropy of the magnetic junctions 120, 122,124, 126 128, and 130. For example, in some embodiments, the long axisof the magnetic junctions 122, 124, 126, and 128 have a long axis of 90nm and a short axis of 60 nm. In some such embodiments, the magneticjunction 120 has a long axis of 125 nm and a short axis of 60 nm. Thejunction 132 has a long axis of 135 nm (horizontally as shown in FIG.2B) and a short axis of 90 nm. In some embodiments, the junctions 122,124, 126, 128, 130, and 132 are 14 nm apart.

FIGS. 2C-2F depict the nonvolatile logic device 100 during switching.The magnetic junction 120 is first switched. This is depicted in FIG.2C. In some embodiments, the input magnetic junction 120 may be switchedusing spin transfer. Thus, a switching current may be driven through themagnetic junction 120. Based on the direction of the current, themagnetic junction 120 may be switched between the two states shown inFIGS. 2B and 2C. In other embodiments, a combination of a current and amagnetic field may be used to switch the magnetic junction 120. Inanother embodiment, a magnetic field only may be used to switch thestate of the magnetic junction 120.

A saturation field may then be applied in the hard axis direction. Themagnetic moments of the junctions 122, 124, 126, 128, and 130 align withthe magnetic field. This situation is shown in FIG. 2D. Upon removal ofthe magnetic field, the moments of the junctions 122, 124, 126, 128 and130 cant away from the hard axis. Because of the interaction between themagnetic junction 120 and the magnetic junction 122, the magneticjunctions 120 and 122 tend to begin to be aligned. This is shown in FIG.2E. The magnetic junctions 122, 124, 126, 128, 130 then align as shownin FIG. 2F. Thus, a change in the state of the input magnetic junction120 is reflected in the output magnetic junction 130.

Because the easy axes of the magnetic junctions 120, 122, 124, 126, 128,and 130 are aligned, the magnetic junction 120 has equilibrium stateswith the magnetic moment parallel or antiparallel to the pinned layer106. Thus, spin transfer may be used to switch the input magneticjunction 120. Inadvertent write and other issues relating to use of amagnetic field to write to the input junction 120 may be avoided.Further, the configuration of the junctions 120, 122, 124, 126, and 128provides wider margins. More specifically, a smaller external field maybe used to saturate the magnetizations of the junctions 122, 124, 126,and 128 along the hard axis. Further, a larger external magnetic fieldmay be used without switching the input junction 120. As a result, alarger range of external magnetic fields may be used to saturate themagnetic junctions 122, 124, 126 and 128 along their hard axes.Programming the nonvolatile logic device 100 may thus be easier.Performance of the nonvolatile logic device 100 may thus be enhanced.

FIGS. 3A-3B depict top and cross-sectional views of another exemplaryembodiment of a nonvolatile logic device 100′. For clarity, FIGS. 3A-3Bare not to scale. The nonvolatile logic device 100′ is analogous to thenonvolatile logic device 100. Consequently, analogous components arelabeled similarly. The nonvolatile logic device 100′ thus includes abottom electrode 102′, an optional pinning layer 104′, a pinned layer106′ including layers 108′, 110′, and 112′, a spacer layer 114′, a toplayer 116′ forming junctions 120′, 122′, 124′, 126′, 128′, 130′, and132′ that correspond to the bottom electrode 102, the optional pinninglayer 104, the pinned layer 106 including layers 108, 110, and 112, thespacer layer 114′, the top layer 116′ forming junctions 120, 122, 124,126, 128, 130, and 132.

The structure and function of the components 102′, 104′, 106′, 108′,110′, 112′, 114′, 116′, 120′, 122′, 124′, 126′, 128′, 130′, and 132′ areanalogous to the structure and function of the components 102, 104, 106,108, 110, 112, 114, 116, 120, 122, 124, 126, 128, 130, and 132,respectively. However, the arrangement of the magnetic junctions 120′,122′, 124′, 126′, 128′, 130′, and 132′ differs. The junctions 120′,122′, 124′, 126′, 128′, and 130′ form a linear array. Stateddifferently, the junctions 120′, 122′, 124′, 126′, 128′, and 130′ arearranged in a line. This is in contrast to the junctions 120, 122, 124,126, 128, and 130, which are not collinear. Instead, the junction 120 isaligned with the junction 122 at a right angle from the line formed bythe remaining junctions 122, 124, 126, 128, and 130.

The nonvolatile logic device 100′ shares the benefits of the nonvolatilelogic device 100. Thus, performance of the nonvolatile logic device 100′is improved. However, note that the increase in the range of theexternal magnetic field may not be achieved.

FIG. 4 depicts a top view of another exemplary embodiment of anonvolatile logic device 200 that is analogous to the nonvolatile logicdevices 100 and 100′. For clarity, only a top view is shown and FIG. 4is not to scale. The nonvolatile logic device 200 is analogous to thenonvolatile logic devices 100 and 100′. Consequently, analogouscomponents are labeled similarly. The nonvolatile logic device 200 thusincludes magnetic junctions 220, 222, 224, 226, 228, 230, and 232 thatcorrespond to the junctions 120, 122, 124, 126, 128, 130, and 132,respectively. Although shown arranged as in the nonvolatile logic device100, the junctions 220, 222, 224, 226, 228, 230 and 232 could bearranged as in the nonvolatile logic device 100′.

The nonvolatile logic device 200 has a magnetic anisotropy (H_(k))gradient. In particular, the H_(k) of the magnetic junctions 222, 224,226, 228, and 230 decreases from the junction 222 to the output junction230. The decrease in H_(k) is monotonic. Thus each junction has a lowerH_(k) than the junction immediately to the left. In order, from highestto lowest H_(k), the junctions are 222, 224, 226, 228, and 230. Themanner in which the Hk decreases may vary. For example, the H_(k) maydecrease linearly or in any other manner. The change in H_(k) in themagnetic junctions 222, 224, 226, 228, and 230 might be due to a changein the shape anisotropy, the magnetic moment, the crystallineanisotropy, an applied field other than that used in switching thenonvolatile logic device, another factor influencing H_(k) or somecombination thereof.

A monotonic decrease in H_(k) between the first magnetic junction 222and the output magnetic junction 230 improves the switchingcharacteristics of the nonvolatile logic device 200. In particular, sucha gradient in H_(k) ensures that the magnetic junctions 222, 224, 226,228, and 230 switch in order. Thus, the magnetic junction 222 closest tothe input junction 220 switches first, then the magnetic junction 224,then the magnetic junction 226, followed by the magnetic junction 228,and then output magnetic junction 230. This results in more reliableswitching.

As discussed above, the input magnetic junction 220 is switched, anexternal magnetic field is applied to saturate the junctions 222, 224,226, 228 and 230, and then the external magnetic field is removed. Whenthe external field is applied, the magnetic junctions 222, 224, 226,228, and 230 saturate in order from lowest H_(k) to highest H_(k). As aresult, the magnetic junction 222 closest to the input magnetic junction220 saturates last. However, all magnetic junctions 222, 224, 226, 228,and 230 are saturated along the hard axis. Upon removal of the externalmagnetic field, the magnetic junction having the highest H_(k) selects astate first. The remaining junctions select their states based on theH_(k), with the highest H_(k) selecting a state first. Thus, themagnetic junction 222 selects its state first. This state selected isbased upon the state of the input magnetic junction 220. Next, themagnetic junction 224 selects its state based upon the state of themagnetic junction 222. The magnetic junction 226 then selects its statebased upon the state of the magnetic junction 224. The magnetic junction228 then selects its state based upon the state of the magnetic junction226. Finally, the output junction 230 selects its state based upon thestate of the magnetic junction 228. Thus, the magnetic junctions 222,224, 226, 228, and 230 select their states in order, with the junctionscloser to the input magnetic junction 220 selecting their state before ajunction further from the input magnetic junction 220. The junctionscloser to the input magnetic junction also influence the magnetic stateof magnetic junctions further from the input magnetic junction. Becausethe magnetic junctions 222, 224, 226, 228, and 230 select their statesin order, information is transferred magnetically from the inputmagnetic junction 220, to the magnetic junction 222, then to themagnetic junction 224, then to the magnetic junction 226, then to themagnetic junction 228, and finally to the output magnetic junction 230.As a result, information is more reliably transferred through thenonvolatile logic device. Thus, the gradient in H_(k) in the junctions222, 224, 226, 228, and 230 may improve reliability of the nonvolatilelogic device 200. Thus, in addition to the other benefits of thenonvolatile logic devices 100 and/or 100′, the nonvolatile logic device200 may be more reliable.

FIG. 5 depicts a top view of another exemplary embodiment of anonvolatile logic device 200′. The nonvolatile logic device 200′ isanalogous to the device 200. For clarity, only a top view is shown andFIG. 5 is not to scale. The nonvolatile logic device 200′ is alsoanalogous to the nonvolatile logic devices 100 and 100′. Consequently,analogous components are labeled similarly. The nonvolatile logic device200′ thus includes magnetic junctions 220′, 222′, 224′, 226′, 228′,230′, and 232′ that correspond to the junctions 120/220, 122/222,124/224, 126/226, 128/228, 130/230, and 132/232, respectively. Althoughshown arranged as in the nonvolatile logic device 100, the junctions220′, 222′, 224′, 226′, 228′, 230′ and 232′ could be arranged as in thenonvolatile logic device 100′.

The nonvolatile logic device 200′ has an H_(k) gradient. In particular,the H_(k) of the magnetic junctions 220′, 222′, 224′, 226′, 228′, and230′ decrease from the input junction 220′ to the output junction 230′.The decrease in H_(k) is monotonic and, in the nonvolatile logic device200′, due to a change in the shape anisotropy. In particular, thelength/long axis of the magnetic junctions 222′, 224′, 226′, 228′, and230′ decreases while the width stays relatively constant. Although notto scale, these changes are shown in FIG. 5. Because of the changes inthe magnetic anisotropy, the nonvolatile logic device 200′ may haveimproved reliability in addition to the other benefits of thenonvolatile logic device 200.

FIG. 6 depicts a top view of another exemplary embodiment of anonvolatile logic device 200″. The nonvolatile logic device 200″ isanalogous to the device 200. For clarity, only a top view is shown andFIG. 6 is not to scale. The nonvolatile logic device 200″ is alsoanalogous to the nonvolatile logic devices 100 and 100′. Consequently,analogous components are labeled similarly. The nonvolatile logic device200″ thus includes magnetic junctions 220″, 222″, 224″, 226″, 228″,230″, and 232″ that correspond to the junctions 120/220/220′, 122/222′,124/224/224′, 126/226/226′, 128/228/228′, 130/230/230′, and132/232/232′, respectively. Although shown arranged as in thenonvolatile logic device 100, the junctions 220″, 222″, 224″, 226″,228″, 230″ and 232″ could be arranged as in the nonvolatile logic device100′.

The nonvolatile logic device 200″ has an H_(k) gradient. In particular,the H_(k) of the magnetic junctions 220″, 222″, 224″, 226″, 228″, and230″ decrease from the input junction 220″ to the output junction 230″.The decrease in H_(k) is monotonic and, in the nonvolatile logic device200″, due to a change in the shape anisotropy. In particular, thewidth/short axis of the magnetic junctions 222″, 224″, 226″, 228″, and230″ increases while the length stays relatively constant. Although notto scale, these changes are shown in FIG. 6. Because of the changes inthe magnetic anisotropy, the nonvolatile logic device 200″ may haveimproved reliability in addition to the other benefits of thenonvolatile logic device 200/200′.

FIG. 7 depicts a top view of another exemplary embodiment of anonvolatile logic device 200′″. The nonvolatile logic device 200′″ isanalogous to the device 200. For clarity, only a top view is shown andFIG. 7 is not to scale. The nonvolatile logic device 200′″ is alsoanalogous to the nonvolatile logic devices 100 and 100′. Consequently,analogous components are labeled similarly. The nonvolatile logic device200′″ thus includes magnetic junctions 220′″, 222′″, 224′″, 226′″,228′″, 230′″, and 232′″ that correspond to the junctions120/220/220′/220″, 122/222′/222″, 124/224/224′/224″, 126/226/226′/226″,128/228/228′/228″, 130/230/230′/230″, and 132/232/232′/232″,respectively. Although shown arranged as in the nonvolatile logic device100, the junctions 220′″, 222′″, 224′″, 226′″, 228′″, 230′″ and 232′″could be arranged as in the nonvolatile logic device 100′.

The nonvolatile logic device 200′″ has an H_(k) gradient. In particular,the H_(k) of the magnetic junctions 220′″, 222′″, 224′″, 226′″, 228′″,and 230′″ decrease from the input junction 220′″ to the output junction230′″. The decrease in H_(k) is monotonic and, in the nonvolatile logicdevice 200′″, due to a change in the magnetic moment. In particular, themagnetic moment of the magnetic junctions 222′″, 224′″, 226′″, 228′″,and 230′″ decreases while the length stays relatively constant. Althoughnot to scale, these changes are shown in FIG. 7. Because of the changesin the magnetic anisotropy, the nonvolatile logic device 200′″ may haveimproved reliability in addition to the other benefits of thenonvolatile logic device 200/200′/200″.

FIG. 8 depicts a side view of another exemplary embodiment of anonvolatile logic device 200″″. The nonvolatile logic device 200″″ isanalogous to the device 200. For clarity, only a top view is shown andFIG. 8 is not to scale. The nonvolatile logic device 200″″ is alsoanalogous to the nonvolatile logic devices 100 and 100′. Consequently,analogous components are labeled similarly. The nonvolatile logic device200″″ thus includes magnetic junctions 222″″, 224″″, 226″″, 228″″,230″″, and 232″″ that correspond to the junctions 122/222′/222″/222′″,124/224/224′/224″/224′″, 126/226/226′/226″/226′″,128/228/228′/228″/228′″, 130/230/230′/230″/230′″, and132/232/232′/232′/232″/232′″, respectively. In addition, although notshown, an input magnetic junction analogous to the input magneticjunctions 220/220′/220″ is also included. Although shown arranged as inthe nonvolatile logic device 100, the junctions 220″″, 222″″, 224″″,226″″, 228″″, 230″″ and 232″″ could be arranged as in the nonvolatilelogic device 100′. Also shown are bottom electrode 202, optional pinninglayer 204, pinned layer 206 including layers 208, 210, and 212, spacerlayer 214, and layer 216 that are analogous to layers 102, 104, 106(including layers 108, 110, and 112), 114, and 116, respectively. Thenonvolatile logic device 200″″ also includes current lines 240, 242,244, 246, 248, and 250 corresponding to magnetic junctions 222, 224,226, 228, 230, and 232, respectively.

The nonvolatile logic device 200″″ has an H_(k) gradient. In particular,the H_(k) of the magnetic junctions 220″″, 222″″, 224″″, 226″″, 228″″,and 230″″ decrease from the input junction (not shown) to the outputjunction 230″″. The decrease in H_(k) is monotonic and, in thenonvolatile logic device 200″″, due to a biasing magnetic field appliedby the lines 240, 242, 244, 246, and 248. In particular, the lines 240,242, 244, 246, and 248 provide a magnetic field that can bias themagnetic junctions 222″″, 224″″, 226″″, 228″″, and 230″″. This biasingmagnetic field acts as an anisotropy on the magnetic junction 222″″,224″″, 226″″, 228″″, and 230″″, respectively. Further, the biasingfields need not be constant. Instead, the fields can be applied atdifferent times. For example, the line 240 might be energized first,followed by the lines 242, 244, 246, and 248 in this order. Further, thetiming of these fields may correspond to the times at which thejunctions 222″″, 224″″, 226″″, 228″″, and 230″″ select their state.Because of the changes in the magnetic anisotropy, the nonvolatile logicdevice 200″″ may have improved reliability in addition to the otherbenefits of the nonvolatile logic device 200/200′/200″/200′″.

FIG. 9 depicts a side view of another exemplary embodiment of anonvolatile logic device 200′″″. The nonvolatile logic device of FIG. 9is substantially the same as the device 200″″ of FIG. 8. However, thelines 240, 242, 244, 246, 248, and 250 have magnetic cladding 252, 254,256, 258, 260, and 262, respectively. The cladding 252, 254, 256, 258,260, and 262 resides on at least the sides and bottoms of the lines 240,242, 244, 246 248, and 250, respectively. Because the cladding 252, 254,256, 258, 260, and 262 is magnetic, the magnetic field provided by thecladding 252, 254, 256, 258, 260, and 262 is enhanced. Thus, themagnetic field provided by the lines 240, 242, 244, 246, and 248 mayalso be increased. Because of the changes in the magnetic anisotropy,the nonvolatile logic device 200′″″ may have improved reliability inaddition to the other benefits of the nonvolatile logic device200/200′/200″/200′″/200″″. Thus, the nonvolatile logic devices 100,100′, 200, 200′, 200″, 200′″, 200″″, and 200′″″ may have improvedperformance and reliability.

FIG. 10 depicts an exemplary embodiment of a method 300 for providing anonvolatile logic device. The method 300 is described in the context ofthe nonvolatile logic device 100. However, other devices including butnot limited to the devices 100′, 200, 200′, 200″, 200′″, 200″″ and/or200′″″ may be formed. The method 300 is described in the context ofparticular steps. However, the steps may be omitted, interleaved,combined, or performed in another manner.

A stack for the magnetic junction is deposited, via step 302. The stackincludes a pinned layer 106, a spacer layer 114, and layers for a freelayer 116. A mask is then provided, via step 304. The mask material isspun on and may include a layer of durimide followed by a layer of amaterial such as hydrogen silsesquioxane (HSQ). HSQ is a negative toneelectron beam resist that may have a high resolution (e.g. on the orderof 10 nm) feature sizes and may be cross-linked by exposure to e-beam orEUV radiation with wavelengths shorter than 157 nm. However, othermaterials might be used. The pattern for the nonvolatile logic device100 is then transferred to the mask. This step may be performed byproviding a photoresist mask, then transferring the pattern to the maskusing an electron beam. The pattern of the mask is transferred to themagnetic junction stack, via step 306. Step 306 may include ion millingthe magnetoresistive stack. In some embodiments, the stack is milledthrough. In other embodiments, such as is depicted in the device 100,only some portion of the layers are milled through. For example, onlythe layer 116 may be milled through. A dielectric is deposited, via step308. For clarity, this dielectric is not depicted in FIGS. 2A-2F. Insome embodiments, the dielectric, such as aluminum oxide, is depositedusing atomic layer deposition (ALD) or may be provided as a spin-onglass.

The nonvolatile logic device 100 is then planarized, via step 310. Thus,the durimide portion of the mask is exposed. In some embodiments, step310 is performed using a chemical mechanical planarization (CMP) or anHSQ process. The mask is removed, via step 312. In some embodiments,step 312 includes etching out the durimide with an oxygen plasma.Contacts may then be provided, via step 314. For example, a mask havingapertures in the locations of the contacts may be provided. Theapertures may be provided using an electron beam. The contacts may thenbe deposited and the mask removed.

Using the method 300, the nonvolatile logic device 100 may be provided.This process is similar to that currently used in fabricating magneticrandom access memories. As such, the method 300 uses well knownprocesses. However, some issues may remain to be worked out.

FIG. 11 depicts an exemplary embodiment of a method 350 for providing anonvolatile logic device. The method 350 is described in the context ofthe nonvolatile logic device 100. However, other devices including butnot limited to the devices 100′, 200, 200′, 200″, 200′″, and/or 200″″may be formed. The method 350 is described in the context of particularsteps. However, the steps may be omitted, interleaved, combined, orperformed in another manner.

A stack for the magnetic junction is deposited, via step 352. The stackincludes a pinned layer 106, a spacer layer 114, and layers for a freelayer 116. A mask is then provided, via step 354. The mask material isspun on and may include a layer of HSQ. The pattern for the nonvolatilelogic device 100 is then transferred to the mask. This step may beperformed by providing a photoresist mask, then transferring the patternto the mask using electron beam lithography. The pattern of the mask istransferred to the magnetic junction stack, via step 356. Step 356 mayinclude ion milling the magnetoresistive stack. In some embodiments, thestack is milled through. In other embodiments, such as is depicted inthe device 100, only some portion of the layers are milled through. Forexample, only the layer 116 may be milled through. A dielectric isdeposited, via step 358. For clarity, this dielectric is not depicted inFIGS. 2A-2F. In some embodiments, the dielectric, such as aluminumoxide, is deposited using atomic layer deposition (ALD) or may beprovided as a spin-on glass.

Vias may then be provided in the insulator, via step 360. The vias maybe opened using electron beam lithography and an oxide reactive ion etch(RIE) process. Contacts may then be provided in the vias, via step 362.For example, a mask having apertures in the locations of the contactsmay be provided. The apertures may be provided using an electron beam.The contacts may then be deposited and the mask removed.

Using the method 350, the nonvolatile logic device 100 may be providedwithout the use of a planarization or additional RIEs. Further, thinvias may be formed. However, additional electron beam patterning is usedto form the vias and the HSQ removed using an RIE.

FIG. 12 depicts an exemplary embodiment of a method 400 for programminga nonvolatile logic device. The method 400 is described in the contextof the nonvolatile logic device 100. However, other devices includingbut not limited to the devices 100′, 200, 200′, 200″, 200′″, and/or200″″ may be programmed using the method 400. The method 400 isdescribed in the context of particular steps. However, the steps may beomitted, interleaved, combined, or performed in another manner.

Referring to FIGS. 2A-2F and FIG. 12, the logic device 100 may start ina particular configuration, shown in FIGS. 2A-2B. Alternatively, thelogic device might start in the state shown in FIG. 2F. The inputmagnetic junction 120 is switched using spin transfer, via step 402. Instep 402, therefore, a current perpendicular-to-plane (CPP) is driventhrough the input magnetic junction 120. The direction of currentdepends upon the state to which the magnetic junction 120 is desired tobe switched. In some embodiments, spin transfer may be used in additionto other switching mechanisms including but not limited to applying afield along the easy axis of the input magnetic junction 120. FIG. 2Cdepicts the nonvolatile memory device 100 after step 402 is performed.

A saturation field is applied in the hard axis direction of the magneticjunctions 122, 124, 126, 128, and 130, via step 404. Thus, the magneticmoments of the junctions 122, 124, 126, 128, and 130 align with themagnetic field. FIG. 2D depicts the nonvolatile device 100 during step404. Note that because the hard axis field is applied, a lower magneticfield may be used.

The saturation field is removed, via step 406. In some embodiments, thefield may be ramped down slowly, while in other embodiments, the fieldmay be cut off more quickly. Upon removal of the magnetic field in step408, the moments of the junctions 122, 124, 126, 128 and 130 cant awayfrom the hard axis. This situation is depicted in FIG. 2E. Because ofthe interaction between the magnetic junction 120 and the magneticjunction 122, the magnetic junctions 120 and 122 tend to begin to bealigned.

After a certain (short) time period, the magnetic moments of themagnetic junctions 122, 124, 126, 128, and 130 align with the easy axisand based upon the alignment after removal of the field. Thus, themagnetic moment for the magnetic junction 122 is aligned with themagnetic moment of the input magnetic junction 120. FIG. 2F depicts thenew equilibrium state of the nonvolatile magnetic logic device. Thus, achange in the state of the input magnetic junction 120 is reflected inthe output magnetic junction 130. As a result, logic operations may becarried out.

Because the easy axes of the magnetic junctions 120, 122, 124, 126, 128,and 130 are aligned, the magnetic junction 120 has equilibrium stateswith the magnetic moment parallel or antiparallel to the pinned layer106. Thus, spin transfer may be used to switch the input magneticjunction 120. Inadvertent write and other issues relating to use of amagnetic field to write to the input junction 120 may be avoided.Further, the configuration of the nonvolatile logic device 100 provideswider margins. More specifically, a smaller external field may be usedto saturate the magnetizations of the junctions 122, 124, 126, and 128along the hard axis. Further, a larger external magnetic field may beused without switching the input junction 120. As a result, a largerrange of external magnetic fields may be used to saturate the magneticjunctions 122, 124, 126 and 128 along their hard axes. Programming thenonvolatile logic device 100 may thus be easier. Performance of thenonvolatile logic device 100 may thus be enhanced.

A method and system for providing and programming a nonvolatile logicdevice has been described. Logic gates may be formed from suchnonvolatile logic devices. The method and system have been described inaccordance with the exemplary embodiments shown, and one of ordinaryskill in the art will readily recognize that there could be variationsto the embodiments, and any variations would be within the spirit andscope of the method and system. Accordingly, many modifications may bemade by one of ordinary skill in the art without departing from thespirit and scope of the appended claims.

We claim:
 1. A nonvolatile logic device comprising: an input magneticjunction including an input junction free layer having an input junctioneasy axis, the input magnetic junction being switchable using a currentdriven through the magnetic junction; an output magnetic junctionincluding an output junction free layer having an output junction easyaxis; and at least one magnetic junction between the input magneticjunction and the output magnetic junction, each of the at least onemagnetic junction including a free layer having an easy axis, the inputmagnetic junction being magnetically coupled to the output magneticjunction through the at least one magnetic junction.
 2. The nonvolatilelogic device of claim 1 wherein the input junction easy axis, the outputjunction easy axis and the easy axis are substantially parallel, each ofthe at least one magnetic junction further including a hard axissubstantially perpendicular to the easy axis.
 3. The nonvolatile logicdevice of claim 1 wherein the input junction easy axis corresponds to aninput junction shape anisotropy, the output junction easy axiscorresponds to an output junction shape anisotropy, and the easy axiscorresponds to a shape anisotropy for each of the at least one magneticjunction.
 4. The nonvolatile logic device of claim 1 wherein the inputmagnetic junction, the at least one magnetic junction, and the outputmagnetic junction form a linear array.
 5. The nonvolatile logic deviceof claim 1 wherein the at least one magnetic junction and the outputmagnetic junction form a linear array, the input junction being alignedwith a first magnetic junction of the at least one magnetic junction ina direction substantially perpendicular to the linear array.
 6. Thenonvolatile logic device of claim 1 wherein the input magnetic junction,the at least one magnetic junction, and the output magnetic junctionshare at least one layer.
 7. The nonvolatile logic device of claim 6wherein the at least one layer includes a pinned layer.
 8. Thenonvolatile logic device of claim 7 wherein the at least one layerincludes a spacer layer.
 9. The nonvolatile logic device of claim 6wherein the spacer layer includes a tunneling barrier layer.
 10. Thenonvolatile logic device of claim 1 wherein the at least one magneticjunction and the output magnetic junction have a plurality of magneticanisotropies decreasing monotonically from the input magnetic junctionto the output magnetic junction.
 11. The nonvolatile logic device ofclaim 10 wherein the at least one magnetic junction and the outputmagnetic junction have a plurality of shape anisotropies correspondingto the plurality of magnetic anisotropies.
 12. The nonvolatile logicdevice of claim 11 wherein each of the at least one magnetic junctionhas a length and a width, the length decreasing from the input magneticjunction to the output magnetic junction.
 13. The nonvolatile logicdevice of claim 11 wherein each of the at least one magnetic junctionhas a length and a width, the width increasing from the input magneticjunction to the output magnetic junction.
 14. The nonvolatile logicdevice of claim 10 further comprising: a plurality of current linescorresponding to the input magnetic junction, the at least one magneticjunction, and the output magnetic junction, the plurality of currentlines corresponding to the plurality of magnetic anisotropies.
 15. Thenonvolatile logic device of claim 14 wherein each of the plurality ofcurrent lines is configured to drive a current corresponding to amagnetic anisotropy of the plurality of magnetic anisotropies.
 16. Thenonvolatile logic device of claim 14 wherein each of the plurality ofcurrent lines is configured to start driving the current at a timecorresponding to the magnetic anisotropy of the plurality of magneticanisotropies.
 17. The nonvolatile logic device of claim 14 wherein atleast a portion of the plurality of current lines includes a primarycurrent conducting portion and a cladding surrounding at least a portionof the primary conducting portion.
 18. A method for providing anonvolatile logic device comprising: providing an input magneticjunction including an input junction free layer having an input junctioneasy axis; providing an output magnetic junction including an outputjunction free layer having an output junction easy axis; and providingat least one magnetic junction between the input magnetic junction andthe output magnetic junction, each of the at least one magnetic junctionincluding a free layer having an easy axis, the input junction easyaxis, the output junction easy axis, and the easy axis beingsubstantially parallel, the input magnetic junction being magneticallycoupled to the output magnetic junction through the at least onemagnetic junction.
 19. The method of claim 18 wherein the input junctioneasy axis, the output junction easy axis and the easy axis aresubstantially parallel, each of the at least one magnetic junctionfurther including a hard axis substantially perpendicular to the easyaxis.
 20. The method of claim 18 wherein the input magnetic junction,the at least one magnetic junction, and the output magnetic junctionform a linear array.
 21. The method of claim 18 wherein the at least onemagnetic junction and the output magnetic junction form a linear array,the input junction being aligned with a first magnetic junction of theat least one magnetic junction in a direction substantiallyperpendicular to the linear array.
 22. The method of claim 18 whereinthe input magnetic junction, the at least one magnetic junction, and theoutput magnetic junction share at least one layer.
 23. The method ofclaim 18 wherein the at least one magnetic junction and the outputmagnetic junction have a plurality of magnetic anisotropies decreasingmonotonically from the input magnetic junction to the output magneticjunction.
 24. The method of claim 18 wherein the input magnetic junctionis switchable using a spin transfer current driven through the inputmagnetic junction.
 25. The method of claim 18 wherein the input magneticjunction is switchable due to an external magnetic field.
 26. A methodfor programming a nonvolatile logic device including an input magneticjunction, an output magnetic junction and at least one magnetic junctionbetween the input magnetic junction and the output magnetic junction,the input junction having an input junction easy axis, the outputjunction having an output junction easy axis, each of the at least onemagnetic junction including a free layer having an easy axis and a hardaxis, the input junction easy axis, the output junction easy axis, andthe easy axis being substantially parallel, the input magnetic junctionbeing magnetically coupled to the output magnetic junction through theat least one magnetic junction, the comprising: switching at least onemagnetic moment of the input magnetic junction from a first state to asecond state; applying at least one magnetic field along the hard axisof the at least one magnetic junction; and removing the magnetic field.27. The method of claim 26 wherein the step of switching the at leastone magnetic moment of the input magnetic junction further includes:driving a current through the input magnetic junction in aperpendicular-to-plane orientation.
 28. The method of claim 27 whereinthe step of switching the at least one magnetic moment of the inputmagnetic junction further includes switching the input magnetic junctionusing spin transfer.
 29. The method of claim 26 wherein the hard axis isperpendicular to the easy axis.
 30. The method of claim 26 wherein theeasy axis is substantially parallel to the input junction easy axis andthe output junction easy axis.